1. Field of the Invention
This invention relates to a process for producing an ink jet head for discharging printing droplets in ink jet printing systems.
2. Related Background Art
Ink jet heads used in ink jet printing systems are commonly provided with fine discharge openings from which printing droplets are discharged, liquid-flow paths, and liquid-discharge energy generating portions. When viewed from the positional relationship between the liquid-discharge energy generating portion and the discharge opening, such ink jet heads are roughly grouped into two forms, one of which is what is called an edge shooter type ink jet head, where the direction of growth of bubbles and the direction of discharge thereof are different, and the other of which is what is called a side shooter type ink jet head, where the direction of growth of bubbles and the direction of discharge thereof are substantially the same. Of these two forms, the side shooter type ink jet head is commonly constructed as shown in FIGS. 8A and 8B.
In FIGS. 8A and 8B, reference numeral 1 denotes a substrate. On this substrate 1, a liquid-discharge energy generating element 2 is provided. Reference numeral 3a denotes a discharge opening from which printing droplets are discharged. In the construction shown in the drawing, two discharge openings are formed, which are provided above two liquid-discharge energy generating elements 2. Thus, in this head, the direction of growth of bubbles and the direction of discharge thereof are substantially the same. The discharge openings 3a are provided in a discharge opening plate 5H, and the discharge opening plate 5H is joined to the substrate 1 via liquid-flow path walls 3H that form a liquid-flow path 3b communicating with the discharge openings.
As a process for producing such a side shooter type ink jet head, for example, a process is known in which a negative type photosensitive dry film is stuck to a substrate provided with the liquid-discharge energy generating element, and the photosensitive dry film is masked in a pattern corresponding to a liquid-flow path and a liquid chamber, which is then exposed to light, followed by development to form the liquid-flow path wall, and next a discharge opening plate 5H produced by electroforming of Ni or the like, provided with the discharge openings, is joined to the substrate via the flow path wall. In this process, however, precise alignment must be made between discharge openings of the discharge opening plate and discharge energy generating elements, and hence a large-sized apparatus for improving assemblage precision is necessary, also requiring complicated production steps. Thus, this process is not so much suited for the bulk production of ink jet heads at a low cost.
Under such circumstances, U.S. Pat. No. 5,478,606 discloses a process in which a soluble resin is used to form a liquid-flow path pattern on a substrate provided with liquid-discharge energy generating elements, then a coating resin layer which is to serve as ink-flow path walls and a discharge opening plate is formed by spin coating, thereafter the coating resin layer is cured and at the same time discharge openings are formed, and finally the pattern is dissolved away. In this process, the discharge openings are formed by photolithography or oxygen plasma etching or using an excimer laser after the coating resin layer has been formed, and hence it is unnecessary to make precise alignment to join the discharge opening plate to the substrate. However, even this process has been sought to be further improved in view of material selectivity and improvement in productivity. More specifically, when photolithography is used to form the discharge opening in the coating resin layer, the coating resin must be a photosensitive resin. Also, when the discharge openings are formed by oxygen plasma etching, it is not only necessary to add the steps of forming and removing a resist mask for the oxygen plasma etching, but also necessary to make treatment for a long time using an expensive apparatus for the dry etching. Also when the discharge openings are formed using the excimer laser, not only it is necessary to use a large-sized expensive apparatus as in the oxygen plasma etching, but also there is a possibility that the discharge openings are reverse-tapered in shape in the direction of discharge.